1. Field of the Invention
The present invention relates to receiving technique in wireless communication, particularly, to a receiver to remove a DC offset component remaining in a received signal, a wireless device using the receiver and a method for cancelling a DC offset component.
2. Description of the Related Art
With a wireless device such as a receiver to be employed in wireless communication, a direct conversion system to directly convert the frequency of a signal received is widely available. With the direct conversion system, since the received signal is multiplied by a local signal to gain an intended baseband signal, a DC offset component may be generated originated from the leak of the local signal so as to deteriorate the receiving performance of the wireless device. In this point of view, it is required that the DC offset component is removed.
Generally, the DC offset component is removed by means of a DC offset canceller. For example, the DC offset canceller may be configured such that the amounts of DC offsets are measured over the range of amplification gain of the intended baseband signal, and stored in a memory per amplification gain. Namely, when the amplification gain is switched, the corresponding DC offset amount is read out from the memory and subtracted from the signal output through the amplifier (Reference 1).
[Reference 1] JP-A 2002-94346 (KOKAI)
In the conventional DC offset canceller as described above, the DC offset component, generated at the amplifier, is removed at the output side of the amplifier. In this point of view, therefore, the DC offset component generated at the input side of the amplifier such as a DC offset component generated at the frequency converter, e.g., to convert a wireless signal into the corresponding baseband signal can not be removed in front of the amplifier in advance. If a signal containing the DC offset component is amplified at the amplifier, the amplification of the signal is saturated due to the DC offset component so that the signal can not be amplified sufficiently. As a result, the receiving performance of the signal may be deteriorated remarkably at the corresponding receiver.
In the case that the gain of the amplifier is high, if the correction value for the DC offset component varies in front of the amplifier after the correction value is converged into a given value, the impulse response may be generated from the amplifier. In this point of view, the receiving performance of the signal may be deteriorated remarkably at the corresponding receiver.